Chapter 9 Lecture Outline Oceans: The Last Frontier
The Vast World Ocean Earth is referred to as the blue planet 71% of Earth s surface is oceans and marginal seas Continents and islands comprise the remaining 29% The Northern Hemisphere is the land hemisphere The Southern Hemisphere is the water hemisphere 81% ocean
The Vast World Ocean
The Vast World Ocean Four main ocean basins 1. Pacific Ocean The largest with the greatest depth 2. Atlantic Ocean About half the size of Pacific and not as deep 3. Indian Ocean Slightly smaller than Atlantic, largely in Southern Hemisphere 4. Arctic Ocean About 7% the size of the Pacific
The Vast World Ocean
Composition of Seawater Salinity The total amount of solid material dissolved in water Dissolved substances in seawater are in such small quantities that expressed in parts per thousand Most of the salt in seawater is sodium chloride Average salinity of seawater - 35
Dissolved Components in Seawater
Composition of Seawater Sources of sea salts Chemical weathering of continental rocks Earth s interior through volcanic eruptions Process called outgassing Composition of seawater has been relatively stable for millions of years Material removed as rapidly as added
Composition of Seawater Processes affecting seawater salinity Changes in water content of the solution Addition of fresh water Precipitation Runoff Icebergs and sea-ice melting Removal of fresh water Evaporation Formation of sea ice Latitude and seasons Surface varies 33 to 38 Extreme. Red Sea- 42
Composition of Seawater
Variations in Temperature and Density with Depth Temperature variations Thermocline Rapid change of temperature with depth Between about 300-1000m Thermo = heat Cline = slope Creates a vertical barrier in ocean column Not present at high latitudes (isothermal)
Variations in Temperature and Density with Depth
Variations in Temperature and Density with Depth Density variations Influenced by salinity Increased salinity = increased density Influenced by temperature Increased temperature = decreased density Greater variations in temperature result in a greater impact of this factor on density Influenced by depth Increased depth = increased density Pycnocline = rapid change of density with depth Not present at high latitudes (isopycnal)
Variations in Temperature and Density with Depth
Variations in Temperature and Density with Depth Layered ocean Layered according to density 3-layer structure Shallow surface mixed zone Transition zone Deep zone Does not exist in high latitudes
An Emerging Picture of the Ocean Floor Bathymetry Mapping ocean depths and the shape, or topography, of the ocean floor HMS Challenger 1872-1876 Traveled to every ocean except Arctic Measured all types of properties, depths Challenger Deep deepest point over 35,000ft
Matthew Fontaine Maury, compiler of winds and currents. Maury was perhaps the first person for whom oceanography was a full-time occupation
An Emerging Picture of the Ocean Floor Echo sounder sonar SOund Navigation And Ranging Invented in the 1920s Primary instrument for measuring depth Reflects sound from ocean floor
An Emerging Picture of the Ocean Floor Multibeam sonar Array of sound sources and listening devices Obtains a profile of a narrow strip of seafloor
An Emerging Picture of the Ocean Floor Satellite altimeter Satellites equipped with radar altimeters Measures variations of the sea surface from space
Kaiko, the deepest-diving vehicle presently in operation, descended to a measured depth of 10,914 meters (35,798 feet) near the bottom of the Challenger Deep on March 24, 1995. The small ROV (remotely operated vehicle) sends information back to operators in the mothership by fiberoptic cable. Kaiko is operated by JAMSTEC, a Japanese marine science consortium.
An Emerging Picture of the Ocean Floor
An Emerging Picture of the Ocean Floor Provinces of the Ocean Floor Three major topographic units 1. Continental margins Passive Active 2. Ocean basin floor Seamount Abyssal plain 3. Mid-ocean ridge Rift valley
An Emerging Picture of the Ocean Floor
Continental Margins Passive continental margins Found along most coastal areas that surround the Atlantic Ocean Not associated with plate boundaries Experience little volcanism Few earthquakes
Continental Margins Passive continental margin features Continental shelf Flooded extension of the continent Varies greatly in width Gently sloping Contains oil and important mineral deposits Some areas mantled by extensive glacial deposits Most consist of thick accumulations of shallow-water sediments
Continental Margins Passive continental margin features Continental slope Marks the seaward edge of the continental shelf Relatively steep structure Boundary between continental crust and oceanic crust
Continental Margins Passive continental margin features Submarine canyons Deep, steep-sided valleys cut into continental slope Some are seaward extensions of river valleys Most appear to have been eroded by turbidity currents Turbidity currents Downslope movements of dense, sediment-laden water Deposits are turbidites
Continental Margins Passive continental margin features Continental rise Found in regions where trenches are absent Continental slope merges into a more gradual incline At base of the continental slope, turbidity currents deposit deep-sea fans
Continental Margins
Continental Margins
Continental Margins Active continental margins Continental slope descends abruptly into a deep-ocean trench Located primarily around the Pacific Ocean Accumulations of deformed sediment and ocean crust form accretionary wedges Some subduction zones have little or no accumulation of sediments
Continental Margins
Continental Margins
Features of Deep-Ocean Basins Deep-ocean trenches Long, relatively narrow features Deepest parts of ocean Most are located in the Pacific Ocean Located at subduction zones Associated with volcanic activity Volcanic island arcs Continental volcanic arcs
Features of Deep-Ocean Basins Abyssal plains Likely the most level places on Earth Sites of thick accumulations of sediment Found in all oceans Seamounts and guyots Isolated volcanic peaks Many form near oceanic ridges May emerge as islands May sink and form flat-topped seamounts called guyots or tablemounts
Features of Deep-Ocean Basins
The Oceanic Ridge Mid-ocean ridge Interconnected ridge system is the longest topographic feature on Earth s surface Over 70,000 km (43,000 mi) in length 23% of Earth s surface Winds through all major oceans Along axis of some segments are deep downfaulted structures called rift valleys
The Oceanic Ridge
The Oceanic Ridge
The Oceanic Ridge Oceanic ridges are characterized by: An elevated position Extensive faulting Numerous volcanic structures that have developed on newly formed crust Consist of layer upon layer of faulted and uplifted basaltic rocks Mid-Atlantic ridge has been studied more thoroughly than any other ridge system
The Oceanic Ridge Elevated position of ridge Due to hot (less dense) newly formed crust Cools, contracts and becomes denser as it moves away from mantle upwelling
Seafloor Sediments Ocean floor is mantled with sediment Sources Turbidity currents Sediment slowly settles to bottom from above Thickness varies Thickest in trenches: up to 10 km Pacific Ocean: 600 m or less Atlantic Ocean: 500 to 1000 m Mud is most common sediment on deepocean floor
Seafloor Sediments Types of seafloor sediments Terrigenous sediment Material weathered from continental rocks Virtually every part of the ocean receives it Fine particles remain suspended for a long time Oxidation often produces red and brown colored sediments
Seafloor Sediments Biogenous sediment Shells and skeletons of marine organisms Most common are calcareous oozes Siliceous oozes composed of skeletons of diatoms and radiolarians Phosphate rich materials derived from bones, teeth, and fish scales
Seafloor Sediments
Seafloor Sediments Hydrogenous sediment Minerals that precipitate directly from seawater Most common types include: Manganese nodules Calcium carbonates Metal sulfides Evaporites
Seafloor Sediments
Seafloor Sediments Distribution Coarse terrigenous deposits dominate continental margin areas Fine terrigenous material common in deeper areas of the ocean basin Hydrogenous sediment comprises only a small portion of deposits in the ocean Few places where very little sediment accumulates (mid-ocean ridges)
Seafloor Sediments A Storehouse of Climate Data Organisms recording climate data become part of the sedimentary record Records of temperature changes revealed in sediment cores from ocean floor